1. Field of the Invention
The present invention relates to a cold forming method of ring-shaped products having a tooth profile such as pulser ring for detection of rotation, external tooth gear, internal tooth gear, and ring-shaped spline.
2. Description of the Prior Art
Ring-shaped products of this type, hitherto, possess a tooth profile formed by machining. Machining however, is poor in productivity and high in manufacturing cost, and therefore plastic deformation processing is desired.
Accordingly, the applicant devised tooth profile forming by squeeze processing as shown in FIG. 14. That is, a material W1 squeezed and formed into a cup shape preliminarily is pushed into a die 51 by using a punch 52, and thereby a tooth profile portion T is processed on the outer peripheral surface of the material W1 by a tooth forming part 53 of tooth profile of the die 51. To form the material W1 into a ring-shaped product, the bottom plate Wa of the material W1 is cut off.
According to this method, the productivity is better than is realized by machining but the material W1 is pulled between the upper end of the tooth forming part 53 of the die 51 and the front end of the punch 52 when forming, and a large tensile stress f acts on a peripheral wall Wb of the material W1, and therefore the peripheral wall Wb of the material W1 is stretched in the axial direction. Accordingly, it is not only difficult to process the formed tooth profile portion T in a sufficient tooth height, but also it was found that the tooth height at the end portion confronting the front end of the punch 52 is lowered due to tapered shrinkage in the tip of the formed tooth profile portion T, thereby failing to obtain an accurate tip shape.